The Lions celebrate a 1-yard touchdown by running back Zach Zenner against the Panthers at Ford ...more

The Lions celebrate a 1-yard touchdown by running back Zach Zenner against the Panthers at Ford Field last season.

Junfu Han, Detroit Free Press

But when Zenner's back finally healed, a recovery that took about six weeks, the running back found himself getting more and more antsy in front of his TV.

"Once you’re healthy that’s when it’s kind of like, 'Wow, well this is getting tougher to watch cause I feel like I could maybe be out there,' " Zenner said.

Zenner spent his days preparing for two realities: One with football and one without.

He worked out twice a day at MECA in Novi, where he trimmed his body fat from 12.6 percent to 8 percent and added 14 pounds of muscle, according to an Instagram post by the gym. And he spent his downtime studying to take the MCAT in March, and possibly attend medical school next year.

Zenner, nicknamed "Doc" by his teammates, studied biology at South Dakota State and intends to become a doctor after his playing career.

"It wasn't that I was done with football it was more, is football done with me?" Zenner said. "So I was preparing for either outcome. Preparing to move on and go to school and do some other fun stuff, and also preparing to come back and play for someone."

Zach Zenner runs by Seahawks linebacker Bobby Wagner during the third quarter of the Lions' 26-6 ...more

Zach Zenner runs by Seahawks linebacker Bobby Wagner during the third quarter of the Lions' 26-6 loss in the playoffs Jan. 7, 2017.

Kirthmon F. Dozier DFP

A few NFL teams called to check in, but it wasn't until Lions general manager Bob Quinn reached out Monday that Zenner knew for sure there was more football to be played.

The team cut Ameer Abdullah on Tuesday and signed Zenner. He went through his first practice Wednesday, and could play Sunday against the Chicago Bears, where he's likely to have his biggest role on special teams.

“I wasn’t ready to be done," Zenner said. "I put so much into getting ready for the season, went through all spring, all training camp. I’d done all the training in the summer, so to have it end right there would have been tough. I’ve invested so much into this year."

Zenner said he still plans to take the MCAT in the spring, but he won't pursue medical school until he's finally finished with football. Scores are typically good for three years, and there's more football to be played.

"It's great to be back," Zenner said. "Hopefully for a while."

Injury update

T.J. Lang (neck) and Darius Slay (knee) missed their second straight practice Thursday because of injury. Lang already has missed games this year with a back injury and concussion, and the Lions' offensive line has played some of its worst football with him out of the lineup. DeShawn Shead likely will be in for a bigger role on defense if Slay can't play.